1. Field of the Invention
The present invention relates to a power converting apparatus and a power converting method, and in particular, relates to a power converting apparatus involving a rectifier and a power converting method.
2. Description of the Related Art
A converter incorporated into a power supply circuit of an air-conditioning equipment and so on is generally used as a single-phase full-wave rectifier circuit. Power factor improvement and suppression of harmonic wave generation are required for the converter. As shown in FIG. 1, a basic circuit of the converter used for the air-conditioning equipment and so on is configured to have a full-wave rectifier circuit (rectifier bridge circuit) 102 connected with an AC power supply 101, and a load 103 such as a DC motor. To such a basic circuit, a smoothing capacitor 104, and a reactor 105 for the power factor improvement (inductive AC impedance) are added. As described in Japanese Laid Open Patent Application (JP-A-Heisei, 10-174442: first conventional example), such a converter has difficulty in obtaining “great power factor improvement effect due to a large phase delay of a fundamental wave, although input current conduction angle extension effect can be expected”, and it is not possible to meet the requirement to the converter because the power factor is low (as an example: 0.75 to 0.8).
A converter in which a voltage boosting circuit is mounted between power supply terminals is shown in the first conventional example. As shown in FIG. 2, in the converter having the voltage boosting circuit, boosting capacitors 107 and 108 are added to the rectifier circuit 102 for the voltage boosting circuit 100. An intermediate node 109 in the voltage boosting circuit is connected through a connection wire 111 to one of AC power input nodes of the rectifier circuit to which AC power is supplied. A two-directional switch 110 is introduced in the connection wire 111. Such a conventional technique has advantages in that the power factor is improved and higher harmonic wave suppression can be attained. However, the technique in the first conventional example inevitably uses the two-directional switch to connect the voltage boosting circuit and the full-wave rectifier circuit. In the technique, a switching frequency is a same extent as a power supply frequency (approximately one to several times the power supply frequency), which is extremely low unlike PWM control. As a result, the technique in the first conventional example effectively overcomes a problem of electromagnetic interference. Consequently, miniaturization and light weight of an apparatus may be possible.
The technique in the first conventional example would be specifically realized as shown in FIG. 3. For realizing the two-directional switch, a specific technique requires a current direction specifying circuit 106 composed of a set of four diodes and a switching element to control connection of electrolytic capacitors 107 and 108 (as an example: 1000 μF at 1500 W). Thus, many parts are required and the part must have a high breakdown voltage because the voltage boosting circuit is used so that the discharge voltage is high. As a result, the production cost increases. Also, main current causes a great loss due to inevitable passage through the two diodes and the switching element. Also, a high harmonic wave problem and a power factor problem are remained.